Undead Swarm. There are 5 zombies in the swarm. For every 20 damage dealt to the swarm, one zombie dies, reducing the effectiveness of the swarm. For every Zombie killed, the Swarm takes a -3 to their attack, and deal 4 less damage on a hit. If 3 Zombies are killed, the swarm loses 10ft of movement speed.

Undead Pile. If the Zombie swarm hits with a melee attack, the enemy must make a Strength Saving Throw equal to the damage dealt before mitigations. On failure, the swarm drags the target to the ground, the target is considered prone and restrained.

Slam. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 20 (5d6 + 5) bludgeoning damage.